This invention relates to infrared filters, and, more particularly, to a tunable infrared filter using no moving parts.
In some applications, a sensor (consisting of a detector, optics, and electronics) is used to image or analyze a scene. Most scenes that are viewed by a sensor present a spectrum of wavelengths of radiation. It is often desirable to base the sensor analysis on only some components of the spectrum, such as a particular band within the infrared portion of the spectrum.
In some applications the wavelengths of interest to be sensed may change with time. A multispectral sensor system is therefore needed to permit selection of the wavelength being analyzed. In one approach, the detector itself could be made controllably sensitive to particular components of the spectrum. However, a multispectral detector for the infrared is expensive and requires the development of electronic detector and readout technology that does not as yet exist. In another approach, multiple sensors can be used, each sensor being most sensitive to a single wavelength band.
In yet another approach, a filter placed between the scene and the detector is used to selectively pass a particular band of wavelengths of radiation of the spectrum. The filter attenuates all components of the spectrum except for those that are to be analyzed. A less complex broadband sensor can therefore be used.
Various types of filters are known in the art. To achieve selectivity of the wavelength to be passed by the filter, it is common practice to utilize a multipart filter, each part passing a single wavelength band. The usual structure of a multipart filter is a filter wheel, with discrete filtering regions positioned around the circumference of the wheel. The wheel is rotated to place the desired filter between the scene and the detector. The filter wheel tends to be large, heavy, and cumbersome. It is therefore not preferred where the entire sensor system must be small and lightweight.
There is a need for an improved filter, for use in a sensor system, which is controllable to permit only a selected wavelength range to be passed. The filter should be small and light in weight, and have no moving parts that require activation, consume large amounts of power, or might be subject to mechanical failure. The present invention fulfills this need, and further provides related advantages.